Towards a voltage tunable two-color quantum-well infrared photodetector

Two-color quantum-well infrared photodetectors (QWIPs), based on electron transfer between coupled QWs, suffer from the presence of the shorter wavelength peak at all bias voltages V-b. We investigate this problem by studying the bias dependence of absorption coefficient alpha and photoconductive gain g as a function of wavelength at 10 K. We fabricate such a detector with a peak wavelength of 8 mum for both bias polarities but a voltage tunable cutoff wavelength (9 mum for V-b>0 and 11 mum for V-b<0). We use corrugated QWIPs with different corrugation periods to extract alpha and g for different values of V-b. We find alphaapproximate to0.1 mum(-1) in the 6-12 mum range with small peaks at 8 and 9.8 mum for V-b>0 and 10 mum for V-b<0. g has a pronounced peak at 7.8 mum for both bias polarities and determines the line shape of the QWIP spectral responsivity. These results are attributed to insufficient electron transfer between the coupled QWs and to low tunneling probability of the longer wavelength photoelectrons. A modified QWIP structure has been proposed for complete switching of spectral responsivity peak when the bias voltage polarity is reversed. (C) 2002 American Institute of Physics.